179
ELECTRON CONFIGURATION (SHORT FORM)
- We can represent the electron configuration without drawing a diagram or writing down pages of
quantum numbers every time. We write the "electron configuration".
# of electrons in the subshell
valence electrons
Valence electrons have the
largest value for "n"!
n
valence electrons
"noble gas core". We're saying that titanium has the same electron
configuration as argon does, with the addition of the electrons that
follow. This is a useful shorthand, since the "core" electrons generally
don't get involved in bonding.
180
ELECTRON CONFIGURATION AND THE PERIODIC TABLE
IA
H
IIA
Li
Be
IIIA IVA VA VIA VIIA He
Na Mg
IIIB IVB VB VIB VIIB
K
Ca Sc Ti
Rb Sr
Y
Zr
V
Ra Ac Rf
IB IIB
VIIIB
Cr Mn Fe Co Ni
B
C
N
O
F
Al
Si
P
S
Cl Ar
Cu Zn Ga Ge As Se Br
Nb Mo Tc Ru Rh Pd Ag Cd In
Cs Ba La Hf Ta W
Fr
VIIIA
Re Os Ir
Db Sg Bh Hs Mt
Pt Au Hg Tl
Sn
Sb Te
Pb Bi
I
"p" block: last electron in these atoms is in a "p" orbital!
"d" block: last electron in these atoms is in a "d" orbital
Kr
Xe
Po At Rn
"inner" transition metals go here
"s" block: last electron in these atoms is in an "s" orbital!
Ne
181
- To write an electron configuration using the periodic table, start at hydrogen,
and count up the electrons until you reach your element!
IA
1
VIIIA
H
IIA
2
Li
Be
3
Na Mg
IIIB IVB VB VIB VIIB
K
IIIA IVA VA VIA VIIA He
"d" block: The d block is shifted DOWN.!
Ca Sc Ti
Rb Sr
Y
Zr
V
Cr Mn Fe Co Ni
Ra Ac Rf
C
N
O
F
Al
Si
P
S
Cl Ar
Cu Zn Ga Ge As Se Br
Nb Mo Tc Ru Rh Pd Ag Cd In
Cs Ba La Hf Ta W
Fr
IB IIB
VIIIB
B
Re Os Ir
Db Sg Bh Hs Mt
Example: Phosphorus (P):
Noble gas core notation for P:
Pt Au Hg Tl
Sn
Sb Te
Pb Bi
I
Ne
Kr
Xe
Po At Rn
"inner" transition metals go here
182
EXAMPLES:
F
S
Cl
Remember - valence electrons are ALL of the
electrons in the outermost SHELL (n)! More that one
subshell (l) may be included in the valence electrons
TITANIUM is a transition metal that commonly forms
either +2 or +4 cations. The 4s electrons are lost
when the +2 ion forms, while the 4s AND 3d electrons
are lost to form the +4!
You can order the subshells in numeric order OR
in filling order
Ti
Se
Noble gas core notation. Use the previous noble gas on the table,
then add the electrons that it doesn't have to the end.
Kr
Sample f-block element
PERIODIC TRENDS
183
- Some properties of elements can be related to their positions on the periodic table.
ATOMIC RADIUS
- The distance between the nucleus of the atoms and the outermost
shell of the electron cloud.
- Relates to the size of the atom.
- As you go DOWN A GROUP (
), the atomic radius INCREASES.
- Why? As you go down a period, you are ADDING SHELLS!
- As you go ACROSS A PERIOD (
), the atomic radius DECREASES
Why? Let's look at some sample atoms.
lithium
Outer electrons
see an
effective +7
charge (shielded
from +9 nucleus
by 2 electrons)
Outer electron
sees an
effective +1
charge (shielded
from +3 nucleus
by 2 electrons)
fluorine
... so fluorine's outer shell is pulled closer to the nucleus than lithium's!
184
(FIRST) IONIZATION ENERGY
- The amount of energy required to remove a single electron from the outer shell
of an atom.
- Relates to reactivity for metals. The easier it is to remove an electron, the more
reactive the metal.
- As you go DOWN A GROUP (
), the ionization energy DECREASES.
- Why? As you go down a period, you are ADDING SHELLS. Since
the outer electrons are farther from the nucleus and charge attraction
lessens with distance, this makes electrons easier to remove as the atoms
get bigger!
- As you go ACROSS A PERIOD (
), the ionization energy INCREASES.
- Why? Let's look at some sample atoms.
lithium
Outer electrons
see an
effective +7
charge (shielded
from +9 nucleus
by 2 electrons)
Outer electron
sees an
effective +1
charge (shielded
from +3 nucleus
by 2 electrons)
fluorine
... since fluorine's outer electrons are held on by a larger effective charge,
they are more difficult to remove than lithium's.
LARGER
IONIZATION
ENERGY
185
THE FIRST TWO PERIODIC TRENDS IN A NUTSHELL
IA
VIIIA
H
IIA
Li
Be
IIIA IVA VA VIA VIIA He
Na Mg
IIIB IVB VB VIB VIIB
K
Ca Sc Ti
Rb Sr
Y
Zr
V
Ra Ac Rf
LARGER SMALLER
RADIUS IONIZATION
ENERGY
IB IIB
VIIIB
Cr Mn Fe Co Ni
B
C
N
O
F
Al
Si
P
S
Cl Ar
Cu Zn Ga Ge As Se Br
Nb Mo Tc Ru Rh Pd Ag Cd In
Cs Ba La Hf Ta W
Fr
SMALLER
RADIUS
Re Os Ir
Db Sg Bh Hs Mt
Pt Au Hg Tl
Sn
Sb Te
Pb Bi
I
Ne
Kr
Xe
Po At Rn
"inner" transition metals go here
186
ELECTRON AFFINITY
- the electron affinity is the ENERGY CHANGE on adding a single electron to an atom.
- Atoms with a positive electron affinity cannot form anions.
- The more negative the electron affinity, the more stable the anion formed!
- General trend: As you move to the right on the periodic table, the electron affinity becomes
more negative.
EXCEPTIONS
- Group IIA does not form anions (positive electron affinity)!
valence electrons for Group IIA!
period number
- To add an electron, the atom must put it into a higher-energy
(p) subshell.
- Group VA: can form anions, but has a more POSITIVE electron affinity than IVA
valence electrons for Group VA!
Half-full "p" subshell! To add an electron, must start
pairing!
- Group VIIIA (noble gases) does not form anions
full "s" and "p" subshells!